1. Field of the Invention
The present invention relates generally to shoes, and, more specifically, to athletic or recreation shoes that comprise a system for preventing serious ankle sprains. Preferred embodiments of the invention comprise an extension that protrudes from the shoe, near the wearer's ankle, to an extent that, when the wearer's foot and ankle begin to invert, the extension impacts the floor or ground to limit or prevent further inversion. Thus, the preferred extension is positioned and sized to prevent serious ankle sprains, but does not impede mobility.
2. Related Art
Ankle sprains are reported to be the cause of approximately 7-10% of all emergency room visits. Ankle sprains are the most common sports injury, and are estimated to be 10-21% of all sports injuries. Athletes participating in basketball, volleyball, soccer, and football are at especially high risk for ankle sprains, which are estimated to be 25-45% of injuries in these sports.
Inversion, eversion, supination, and pronation are events/actions that primarily occur at the subtalar joint. Inversion may be described as the inward turning of the sole of the foot, and eversion may be described as the outward turning of the sole of the foot. Supination is a combination of calcaneal inversion, foot adduction (moving of a body part toward the central axis of the body), and plantar flexion. Pronation is a combination of calcaneal eversion, foot abduction (to draw away from the central axis of the body), and dorsiflexion. Therefore, the events/actions that will be limited or remedied by preferred embodiments of the invention will fall under the categories of inversion or supination.
The most common ankle injury is a lateral sprain caused by inversion of the foot, which is the turning inward of the foot relative to its natural position wherein the sole of the foot is substantially flat on a horizontal surface and the plane through the center of the heel (parallel to the length of the foot) is vertical. Lateral ankle sprains are also referred to as “inversion,” or sometimes “supination,” ankle sprains, and the motion that results in said sprains is often referred to as “foot inversion” and sometimes also “ankle inversion”. It has been reported that 85% percent of ankle injuries are sprains, and 85% of those are lateral sprains. More than approximately 25,000 lateral ankle sprains are believed to occur each day in the United States.
The most common mechanism of ankle injury is an athlete who “rolls” over the outside of his or her ankle, “turning” his/her ankle and injuring the lateral-ligament complex by stretching or tearing the ligaments, with the result being an “ankle sprain.” This usually occurs as either a non-contact injury, or when the athlete lands from a step or jumps onto an opponent's foot with an inverted foot. The foot is usually plantar-flexed at the time of such an injury.
Because the inner ankle is more stable than the outer ankle, the foot is likely to turn inward (foot inversion) from a fall, tackle, or jump. Therefore, athletes who jump during their sport therefore are at high risk for ankle sprains because they can accidentally land on the side of their foot, or because they can accidentally land on another player's foot. Extensive running, exercise, or training also can overstress the ligaments, leading to injury. Contact and kicking sports expose the foot and ankle to potential trauma-direct blows, crushing, displacement, etc. Sprains are especially prevalent in football, hockey, and soccer, wherein trauma to the ankle can dislocate a joint, fracture a bone, stretch or tear ligaments, or strain muscles and tendons.
In barefoot conditions, the ankle and foot normally avoid an external inverting torque because the line of action of the reaction force is seldom far from the subtalar axis. A shoe may make the foot more vulnerable to hyperinversion because the added breadth/thickness of the shoe increases the length of the lever aim that, in effect, allows/causes the force acting on the foot to invert the foot. Further, the friction between the shoe and the ground adds a shear (horizontal)-force component, thus creating more torque about the subtalar joint. In a traumatic situation, an external inversion torque typically starts the mechanism of injury. If the evertor muscles cannot counteract the external inversion torque, hyperinversion resulting in trauma to the lateral ankle ligaments is likely to occur.
The bony and soft tissue anatomy of the ankle places the lateral side of the ankle at higher risk than the medial side. The distal end of the fibula (ie, the lateral malleolus) extends further inferiorly than the distal end of the tibia (ie, the medial malleolus). This discrepancy in length gives the medial ankle superior stability by improving bony resistance to eversion (outward movement of foot relative to its normal position, as opposed to the inward movement of the foot in inversion).
Although athletes usually recover quickly from ankle sprains, failure to rehabilitate appropriately imposes an increased risk for future injury. The first time a person sustains a sprain, the ligaments are stretched and typically the person will be more prone to “lateral ankle instability” and future ankle sprains. Such a person typically needs a brace for support or surgery to repair the ligaments. Therefore, the most common predisposition to suffering a lateral ankle sprain is the history of at least one previous ankle sprain. In sports such as basketball, recurrence rates have been reported to exceed 70%. Repetitive sprains have also been linked to increased risk of osteoarthritis and articular degeneration at the ankle.
A factor in determining whether a sprain will occur, and how severe the sprain will be, is the rate and magnitude of “loading” on the foot and/or ankle, which may also be described as the rate of application of the force and the amount of overall external force to which the foot/ankle is subjected during the event (typically, an outward force). Another factor, as discussed elsewhere in this document, is the overall health and strength of the foot and ankle, and the associated ligaments and muscles, which may determine the speed and strength with which the said foot, ankle, ligaments and muscles resist the externally applied forces. The response to the rate of loading, the rate of inversion, and the ability of the human body to react, compensate, and correct the inversion, are all interrelated factors in determining the severity of the resulting injury. In simple terms, when the rate of loading and the rate of inversion are fast, the body has less time to react, resulting in increased inversion and probably in increased injury. Also, if the human body is slower and/or weaker in its reaction, because of innate ability, age, or previous injuries, increased inversion and probably increased injury will result.
A discussion of rate of loading and rate of inversion, and the effects of shoe type, is presented in Ricard, et al. “Effects of High-Top and Low-Top Shoes on Ankle Inversion.” Journal of Athletic Training. 2000: 35(1); 38-43. As suggested by this article, high-top shoes may be effective in reducing the amount and rate of inversion. Also, wrapping, braces, or other reinforcements may be effective in reducing the amount and rate of inversion, but, in the inventor's opinion, said reinforcements may also reduce mobility of the wearer.
Shoes with stabilizing features, or broadened soles, are described in the patent literature. Examples include Katz, et al. (U.S. Pat. No. 6,775,929, issued Aug. 17, 2004) discloses a stabilization device for a shoe that comprises small lateral bumpers, which extend from the sole of the shoe, at or very near to the plane of the bottom of the sole. Dupree (U.S. Pat. No. 5,875,569, issued Mar. 2, 1999) discloses a small “wing” that extends outwardly from the lateral side of the sole of the shoe between the ankle and the ball of the user's foot, wherein the wing is very near to the bottom of the sole so that the wing contacts the floor/ground almost immediately upon the beginning of any inversion. Ellis, III (U.S. Pat. No. 6,163,982) and Mathieu, et al. (U.S. 2007/0068046 A1) disclose shoe soles that are broader than those considered normal and that may have some stabilizing effect. Weaver, III (U.S. Pat. No. 6,964,119) discloses spring members that extend from the shoe upper down to the plane of the sole, as a part of an energy storage system that Weaver describes as converting impact force generated by the user at the heel portion, due to natural walking or running motion, into propulsion forces to thereby enhance the user's performance.
There is still a need for a shoe that helps prevent foot/ankle inversions, or that helps lesson the seriousness of said foot/ankle inversions and the consequent injuries. The inventor believes that there is a need for such a shoe that also allows excellent mobility and comfort, to minimize or eliminate the anti-inversion system's interference with the sports or other activities of the wearer.